In general, blood pressure refers to the pressure of blood against the wall of a blood vessel, and a heart alternates between contraction and relaxation about 60 to 80 times a minute. The pressure applied to the blood vessel when the heart contracts to push out blood is called ‘systolic blood pressure’ and also called ‘maximal blood pressure’ since the blood pressure is the highest. Further, the pressure maintained in the blood vessel when the heart is relaxed to receive blood is called ‘diastolic blood pressure’ and also called ‘minimal blood pressure’ since the blood pressure is the lowest.
Usually, a normal person has a systolic blood pressure of 120 mmHg and a diastolic blood pressure of 80 mmHg. In Korea, one or more in four adults have high blood pressure and this proportion rapidly increases after the age of 40.
The high blood pressure becomes a problem since it can lead to life-threatening complications such as eye diseases, renal diseases, artery diseases, brain diseases and heart diseases if the high blood pressure is left untreated. Therefore, the consistent measurement and management of the blood pressure are needed for a hypertensive patient who is at risk for the complications or has the complications.
With recent increased concern over health, various kinds of blood pressure measuring devices have been developed.
As a method of measuring the blood pressure, there are a Korotkoff sounds method, an oscillometric method, a tonometric method, etc.
The Korotkoff sounds method is a typical pressure measuring method, in which a body part where arterial blood flows is compressed enough to stop the flow of the blood and then the pressure at a moment when a pulse first sounds is taken as systolic pressure and the pressure at a moment when the pulse sound disappears is taken as diastolic pressure while the blood pressure is lowered.
The oscillometric method and the tonometric method are methods applicable to a digital blood pressure measuring device.
Like the Korotkoff sounds method, the oscillometric method sufficiently presses the body part where the arterial blood flows, so that the flow of the arterial blood can be stopped. Then, pulse waves, generated while the blood pressure is lowered at a constant speed or while the blood pressure of the body part is raised at a constant speed, are sensed, thereby taking the systolic pressure and the diastolic pressure.
In this method, pressure that has a constant level as compared with the maximum amplitude of the pulse wave may be taken as the systolic pressure or the diastolic pressure, or pressure of when the pulse wave amplitude is rapidly changed may be taken as the systolic pressure or the diastolic pressure.
Further, while the body part is compressed and then decompressed at a constant speed, the systolic pressure is measured earlier than the moment when the pulse wave has the maximum amplitude and the diastolic pressure is measured later than the moment when the pulse wave has the maximum amplitude. On the other hand, while the compression is increased at a constant speed, the systolic pressure is measured later than the moment when the pulse wave has the maximum amplitude and the diastolic pressure is measured earlier than the moment when the pulse wave has the maximum amplitude.
Next, the tonometric method refers to a method of successively measuring the blood pressure based on the amplitude and shape of a pulse wave generated when a body part is compressed not to completely stop the flow of the arterial blood.
As described above, a blood pressure monitor for measuring the blood pressure is the most basic medical device for taking the blood pressure as a basic health index, and is thus not only almost essentially provided in general clinics and hospitals but also well used at home, a sport center, etc. to measure personal blood pressure.
However, most of conventional blood pressure monitors have been produced as a forearm style that the blood pressure monitor is wound around an upper arm (or a portion from a shoulder to an elbow) and measures the blood pressure whenever there is a need of measuring the blood pressure. Accordingly, the blood pressure monitor is inconvenient to carry and is not easy to measure the blood pressure anytime a user wants.
For example, the existing blood pressure monitor based on the oscillometric method has been produced as only the forearm style, and thus needs a blood pressure monitor main body wound around and compressing a forearm, a pressure cuff, a tube plug, an air hose, etc. Therefore, a conventional blood pressure monitor has a complicated structure and is bulky. Further, it is cumbersome to use the conventional blood pressure monitor since there are many preparations for measurement, for instance, the air hose has to be fitted to face down for correct measurement, the cuff has to be mounted being higher than the elbow by 1-2 cm, and so on.
In particular, change in the blood pressure is varied depending on physical features of an examinee, and therefore a patient who has complications has to check his/her blood pressure periodically and/or directly when s/he feels sick. However, a mercury blood pressure monitor and an electronic blood pressure monitor are inconvenient for the patients due to the following problems.
First, the mercury blood pressure monitor and the electronic blood pressure monitor employ the cuff that requires air injection. However, the cuff is so bulky that it is cumbersome for a user to wear the cuff in real time.
In addition, the mercury blood pressure monitor employing a pneumatic cuff is so bulky and heavy that it is impracticable for an examinee (i.e. a patient), who has to frequently measure his/her blood pressure, to always carry. Further, it is cumbersome to attach and detach the blood pressure monitor whenever there is a need of checking the blood pressure.
Although there has been proposed a pneumatic electronic blood pressure monitor having the same accuracy as the foregoing conventional blood pressure monitor, it is heavy and bulky since an electric pump and an air injection cuff are employed and thus causes a patient not to move freely if he or she has to carry the blood pressure monitor and periodically check his/her blood pressure.
Besides, there have been proposed pressureless electronic blood pressure monitors that measure the blood pressure based on pulses at a wrist or a fingertip and various parameters. However, such a pressureless electronic blood pressure monitor has low precision since it is difficult to correctly specify and universally offer the parameters, and is hardly applicable to patients who have to periodically and accurately check his/her blood pressure.
In addition, a blood pressure monitor mounted to a wrist and capable of measuring the blood pressure has recently been released under the name of wrist watch style blood pressure monitor.
However, the existing wrist watch style blood pressure monitor is not small enough in volume to be mounted to a wrist like a watch even though it is called the wrist watch style for no other reason but being mounted to the wrist for measuring the blood pressure.
That is, the conventional wrist watch style blood pressure monitor has been achieved by only reducing the size of the conventional blood pressure monitor so as to be applicable to a wrist instead of an upper arm since the blood pressure is measured in such a way of wearing a pressure cuff and operating a pump.